Antenna device

ABSTRACT

An antenna device having a magnetic core to be surface-mounted on a circuit substrate includes a pair of coil portions spaced apart from each other at a predetermined interval. The coil portions are connected by a connecting conductor. An end of the magnetic core includes a curved or bent portion curved toward the circuit substrate. This structure defines an RFID antenna device having an improved receiving sensitivity that can be surface-mounted without increasing the thickness of a casing of a mobile electronic device.

BACKGROUND OF THE INVENTION

The present invention relates to antenna devices that can be utilized asan antenna in mobile electronic devices, for example.

DESCRIPTION OF THE RELATED ART

As disclosed in, for example, Japanese Unexamined Patent ApplicationPublication No. 2004-153463 and Japanese Unexamined Patent ApplicationPublication No. 2006-050522, antenna coils are mounted in casings ofmobile electronic devices, such as mobile phones, that are equipped withRFID (Radio Frequency Identification) radio tags communicating withexternal devices via electromagnetic signals.

According to Japanese Unexamined Patent Application Publication No.2004-153463, data carrier signals from the outside are received by anantenna coil mounted on a substrate included in a mobile phone so as totransmit and receive data in a non-contact manner to and from areader/writer. The antenna coil of Japanese Unexamined PatentApplication Publication No. 2004-153463 is a substantially planar coiladhered to a planar magnetic core. The antenna coil is mounted so thatthe axial direction of the antenna coil is substantially perpendicularto the mounting substrate, that is, the axial direction is substantiallyperpendicular to a plane of the casing of the mobile phone terminal.

An antenna coil according to Japanese Unexamined Patent ApplicationPublication No. 2006-050522 is used as an antenna for radio-controlledclocks and RFID systems, and is disposed inside a casing. A coil of thisantenna coil is wound around a magnetic core made of a magnetic body.Ends of the magnetic core of the antenna coil are bent in a directionaway from the adjacent casing or a metal portion of the adjacent casing.Such a configuration enables many magnetic fluxes entering the casing toconverge, which enables the antenna to be highly sensitive.

Systems for checking tickets by prompting users to place RFID-equippedmobile phones having the aforementioned antenna coils, instead ofcommuter passes, over automated ticket gates and exchanging userinformation have been proposed. Generally, users place a principalsurface of mobile phone terminals in a substantially horizontalorientation over a detecting surface of a reader/writer. In this case,the majority of the magnetic fluxes that radiate from the reader/writerenter the mobile phone in a direction substantially vertical to theprincipal surface of the mobile phone. A liquid crystal display panel, akeyboard, an RF circuit substrate, and a battery are included in acasing of mobile phone. Since these components have a substantiallyplanar ground electrode, the magnetic fluxes that are substantiallyperpendicular to the principal surface of the mobile phone terminalscannot penetrate the mobile phone terminals.

An antenna coil described in Japanese Unexamined Patent ApplicationPublication No. 2004-153463 is mounted so that the coil axis issubstantially perpendicular to a principal surface of a circuitsubstrate. Accordingly, when the aforementioned communicationconfiguration is used, the magnetic fluxes entering the casing of themobile phone terminals are transmitted through the coil axis of theantenna coil, which can induce the current in the antenna coil. However,since a lateral area of the magnetic core is relatively small inJapanese Unexamined Patent Application Publication No. 2004-153463, theradiation efficiency of the magnetic fluxes transmitted through theantenna coil is relatively low. Accordingly, it is difficult for themagnetic fluxes to enter the mobile phone and the current caused in theantenna coil is significantly weak. Accordingly, there is a problem inthat the optimum antenna sensitivity cannot be achieved.

On the other hand, an antenna coil described in Japanese UnexaminedPatent Application Publication No. 2006-050522 is configured so that thecoil axis is substantially parallel to a principal surface of a circuitsubstrate. Since a coil is wound around a central portion of a magneticcore in the antenna coil described in Japanese Unexamined PatentApplication Publication No. 2006-050522, magnetic fluxes can enter thebent ends not having the winding coil. When users place mobile phoneover a reader/writer of automated ticket gates, the users generallyintends to place a central portion of the mobile phone terminals overthe reader/writer. However, since the antenna coil described in JapaneseUnexamined Patent Application Publication No. 2006-050522 is configuredto receive the magnetic fluxes at the ends thereof, the current inducedin the antenna coil by the incoming magnetic fluxes is relatively weakwhen the central portion is placed over the reader/writer. That is, thepossibility of successful communication with automated ticket gates thatfunction as readers/writers becomes very low. When the communicationwith the automated ticket gates is not performed successfully, theautomated ticket gates block users of the mobile phone from entering.Since the number of people passing through the automated ticket gatesper unit of time during rush hours in metropolitan areas is extremelyhigh, major disruptions may occur when the automated ticket gate systemsfrequently block the human flow due to a communication failure.

To improve communication performance of such antenna coils, the antennacoil described in Japanese Unexamined Patent Application Publication No.2006-050522 may be mounted so that the coil axis is substantiallyperpendicular to the principal surface of the mobile phone. However,such a mounting method causes a problem of an increase in the thicknessof the casing. Even if the antenna coil can be disposed in this manner,the aforementioned ground electrode is provided at the central portionof the mobile phone. Thus, to avoid the influence thereof, the antennacoil must be disposed at a corner portion of the mobile phone. Asmentioned above, when users place mobile phone terminals over areader/writer of automated thicket gates, the users intend to place thecentral portion of the mobile phone terminals over the reader/writer.The possibility that the coil axis of the antenna coil of the mobilephone terminals is shifted from an area of the reader/writer thatenables the most efficient communication is increased, and there is aproblem in that it is difficult to maintain an optimum communicationstate.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide antenna devices that can be surface-mounted ona circuit substrate of a mobile phone or mounted inside a casing, thatcan decrease the thickness, and that can achieve favorable communicationwith a reader/writer.

A preferred embodiment of the present invention includes an antenna coilincluding a magnetic core that has a first principal surface and asecond principal surface facing the first principal surface and that hasa curved or bent (simply referred to as “curved” herein) portion at atleast one end of the magnetic core, and a coil disposed on the firstprincipal surface of the magnetic core, a coil axis being substantiallyperpendicular to the first principal surface, and an opening disposed ata central portion of the coil, and a circuit substrate. The antenna coilis mounted on the circuit substrate such that the second principalsurface of the magnetic core faces amounting surface of the circuitsubstrate.

Another preferred embodiments of the present invention includes anantenna coil including a magnetic core having a curved portion at atleast one end of the magnetic core, and a coil that is wound around themagnetic core and that is defined by a coil portion A and a coil portionB connected with each other at a predetermined interval, and a circuitsubstrate. The curved portion is provided at an end of the magnetic corelocated in a direction of the coil axis of the coil. The antenna coil ismounted on the circuit substrate such that the coil axis is parallel orsubstantially parallel to a principal surface of the circuit substrate.

Preferably, the curved portion is disposed in a direction along alateral surface of the circuit substrate.

Preferably, at least a portion of an end surface of the curved portionis located outside the circuit substrate in plan view.

The antenna coil is preferably mounted on the circuit substrate with aninterval therebetween.

Preferably, a flexible substrate having an electrode pattern providedthereon is wound around the magnetic core to define the coil.

Preferably, the antenna coil includes an electrode film, which isinsulated from the coil, on a surface of the magnetic core that facesthe circuit substrate.

The coil portion A and the coil portion B are preferably wound arounddifferent magnetic cores, and coil axes of the coil portion A and thecoil portion B are preferably substantially coincident.

According to a preferred embodiment of the present invention, the coilportion A and the coil portion B are preferably wound around differentmagnetic cores, and coil axes of the coil potion A and the coil portionB are shifted such that at least a portion of a coil section of the coilportion A and a coil section of the coil portion B that are projectedonto a given plane overlap one another.

Preferably, the coil portion A and the coil portion B are connected byan electrode pattern provided on the circuit substrate.

Alternatively, the coil portion A and the coil portion B may preferablybe connected by an electrode pattern provided on a substrate differentfrom the circuit substrate.

The coil portion A and the coil portion B are preferably connected sothat an electromotive force is not caused by common magnetic fluxes thatpenetrate in a direction of the coil axis.

Coil winding directions of the coil portion A and the coil portion Baround the coil axis are preferably different from one another.

According to various preferred embodiments of the present invention,antenna devices that can be surface-mounted on a circuit substrate of amobile phone terminal or mounted inside a casing, and that have adecreased thickness can be obtained. In addition, since the magneticreluctance at an end of an antenna coil is reduced, magnetic fluxesentering the antenna coil can pass through a magnetic core more easily.This improves the sensitivity of the antenna, and antenna devices thatachieve favorable communication with a reader/writer can be obtained.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an antenna device describing a firstpreferred embodiment of the present invention.

FIG. 2 is a perspective view of an antenna device describing a secondpreferred embodiment of the present invention.

FIG. 3 is a conceptual sectional view describing a principle of anoperation of a preferred embodiment of the present invention.

FIG. 4 is a perspective view of an antenna device describing a thirdpreferred embodiment of the present invention.

FIG. 5 is a perspective view of an antenna device describing a fourthpreferred embodiment of the present invention.

FIG. 6 is a perspective view of an antenna device describing a fifthpreferred embodiment of the present invention.

FIG. 7 is a perspective view of an antenna device describing a sixthpreferred embodiment of the present invention.

FIG. 8 is a perspective view of an antenna device describing a seventhpreferred embodiment of the present invention.

FIG. 9 is a sectional view of an antenna device describing an eighthpreferred embodiment of the present invention.

FIG. 10 is a perspective view of an antenna device describing a ninthpreferred embodiment of the present invention.

FIG. 11 is a plan view of a flexible substrate according to the ninthpreferred embodiment of the present invention.

FIG. 12 is a perspective view of an antenna device describing a tenthpreferred embodiment of the present invention.

FIG. 13 is a plan view of a flexible substrate according to the tenthpreferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the drawings.

A first preferred embodiment will be described with reference to FIG. 1.FIG. 1 is a perspective view of an antenna device 106 that is a firstpreferred embodiment of the present invention.

An antenna coil 206 is provided on a principal surface of a circuitsubstrate 1. The antenna coil 206 can preferably be readily adhered tothe circuit substrate 1 using an adhesive or a double-sided adhesivetape, for example. The circuit substrate 1 preferably is a substrateprovided in a mobile phone. An RF circuit and a control circuit, notshown, are provided on the circuit substrate 1. The circuit substrate 1is arranged in a casing to be substantially parallel to a principalsurface of the mobile phone terminal. In addition, a ground electrode(not shown) is provided on substantially the entire surface of thecircuit substrate 1 that faces a surface on which the antenna coil 206is disposed.

The antenna coil 206 is defined by a magnetic core 60 and a coil 70. Themagnetic core 60 has a first principal surface and a second principalsurface. The first principal surface faces the second principle surface,while the second principal surface faces the circuit substrate. Inaddition, curved portions 61 and 62 that are arranged along lateralsurfaces of the circuit substrate 1 are provided at both ends of themagnetic core 60. That is, the magnetic core 60 curves or bends near thelateral surfaces of the circuit substrate 1. Since the magnetic core 60curves so as to sandwich the circuit substrate 1, end surfaces of themagnetic core 60 are not disposed on the circuit substrate 1. The endsurfaces of the magnetic core mean surfaces facing a curving directionof the magnetic core and are located at leading ends of the magneticcore. In this preferred embodiment, the end surfaces indicate surfacesof the curved portions 61 and 62 that are arranged substantially inparallel to the circuit substrate 1. The coil 70 includes a coilconductor 65 disposed on the first principal surface of the magneticcore 60 that does not face the circuit substrate 1. The coil 70 has ashape of a spiral on the surface, and the coil axis thereof isperpendicular or substantially perpendicular to the first principalsurface of the magnetic core 60. An opening 63 not including the coilconductor 65 is disposed at the approximate center of the coil 70. Byproviding the opening 63, the coil conductor 65 does not preventmagnetic fluxes from passing into the antenna coil 206, and the magneticfluxes from the direction perpendicular or substantially perpendicularto the first principal surface of the magnetic core 60 are allowed topass through. A through hole is disposed at a conductor end 66 of thecoil 70. The conductor end 66 of the coil 70 is electrically connectedto an electrode (not shown) disposed on a surface of the circuitsubstrate 1 that faces the antenna coil 206 by soldering, for example,and is ultimately connected to a terminal 7. A conductor end on a sideopposite to the side of the conductor end 66 of the coil 70 is connectedto a terminal 8. The terminals 7 and 8 are preferably pattern electrodesthat are provided on the circuit substrate 1, and are connected to anRFID processing circuit, not shown, on the circuit substrate 1.

Magnetic fluxes from above the antenna device 106 pass into the coilopening 63, and induce the current in the coil 70. By making the coilopening 63 larger, the incoming magnetic fluxes increase and the inducedcurrent is increased, which is thus preferable. The magnetic fluxes thatare passed into the magnetic core 60 cannot penetrate the circuitsubstrate 1 since a ground electrode is provided on the circuitsubstrate 1. The magnetic fluxes branch off in the magnetic core 60, andpass outside primarily from the curved portions 61 and 62. Since themagnetic core 60 includes the curved portions 61 and 62 at both endsthereof, a section perpendicular or substantially perpendicular to eachprincipal surface is larger at the ends of the magnetic core 60.Accordingly, the magnetic reluctance at the ends of the magnetic core 60is decreased and the magnetic fluxes can pass through the magnetic core60 more easily. In addition, since the end surfaces of the curvedportions 61 and 62 are not disposed on the circuit substrate 1 and arelocated outside of the circuit substrate 1, the magnetic fluxes areradiated from substantially the entire surface of the curved portionsincluding the end surfaces. Accordingly, the structure providessignificantly high radiation efficiency of the magnetic fluxes andenables the magnetic fluxes to pass through the magnetic core 60 moreeasily. Since the coil 70 preferably has a substantially spiral shape onthe first principal surface of the magnetic core 60 in this preferredembodiment, it is possible to make the magnetic core 60 thinner ascompared to the following preferred embodiments.

A second preferred embodiment will be described with reference to FIG.2. FIG. 2 is a perspective view of an antenna device 100 that is asecond preferred embodiment of the present invention. The same numeralsare applied to the same portions as those of FIG. 1, and the descriptionthereof is omitted.

An antenna coil 200 is disposed on a circuit substrate 1. A magneticcore 2 is provided in the antenna coil 200. Both ends of the magneticcore 2 curve near lateral surfaces of the circuit substrate 1 so as todefine curved portions 20 and 21 that extend in a direction along thelateral surfaces of the circuit substrate 1. A coil conductor 4 and acoil conductor 5 are wounded around the magnetic core 2, therebydefining a coil portion A and a coil portion B at a portion of themagnetic core 2 excluding the curved portions 20 and 21. The coilportion A and the coil portion B define a pair of coils. The curvedportions 20 and 21 are arranged in a direction of coil axes of the coilportion A and the coil portion B. In addition, the coil axes of the coilportion A and the coil portion B are substantially parallel to amounting surface of the circuit substrate 1, and are preferablysubstantially coincident with one another. Although only eight turns ofthe winding are shown in each coil portion for convenience ofdescription, the number of turns is not limited to this. The coilportion A and the coil portion B are spaced apart from one another by apredetermined interval d, and a non-coil portion 3 is providedtherebetween. The non-coil portion 3 allows magnetic fluxes to pass intothe magnetic core 2. The right end of the coil portion A and the leftend of the coil portion B are serially connected by a connectingconductor 6 to define a pair of coils. The coil conductors 4 and 5 andthe connecting conductor 6 defining the pair of coils are preferablyformed by a single copper wire. The copper wire is wound around themagnetic core 2, whereby the coil portion A and the coil portion B areformed. Since winding directions around the coil axes of the coilportion A and the coil option B are opposite to one another, the coildoes not induce a current in response to magnetic fluxes that penetratethe magnetic core along both coil axes. A terminal 7 is connected to astarting end (or a terminating end) of the coil portion A, and aterminal 8 is connected to a terminating end (or a starting end) of thecoil portion B. The terminals 7 and 8 and the ends of the coils canpreferably be electrically connected by soldering, for example. Theterminals 7 and 8 are pattern electrodes provided on the circuitsubstrate 1, and are connected to an RFID processing circuit, not shown,on the circuit substrate 1.

FIG. 3 is a conceptual sectional view along the coil axis of the antennadevice 100 shown in FIG. 2. In FIG. 3, the same numerals are applied tothe same portions as those of FIG. 2, and the description thereof isomitted.

Magnetic fluxes 300 and 301 from above the antenna device 100, i.e.,from a principal surface of a mobile phone cannot penetrate the circuitsubstrate 1 because a ground electrode is disposed on the circuitsubstrate 1. The magnetic fluxes 300 and 301 enter the magnetic core 2through the non-coil portion 3 disposed between the coil portion A andthe coil portion B of the antenna coil 200, and pass through themagnetic core 2 along the coil axis, and go out from end faces 9 and 10.In this preferred embodiment, the end surfaces 9 and 10 mean surfacesextending a curving direction of the magnetic core 2 and are located atleading ends of the magnetic core 2. Since outer sides of the coilportion A and the coil portion B of the magnetic core 2 are bent towardthe side of the circuit substrate 1, a CC-cross section and a DD-crosssection become larger, due to which, the magnetic reluctance at theexits of the magnetic fluxes reduces and the magnetic fluxes can passthrough the magnetic core 2 more easily. Similar advantages can beobtained when the magnetic core is bent toward a side opposite to thecircuit substrate 1. When the magnetic core is bent toward the side ofthe circuit substrate 1, components of the magnetic fluxes 300 and 301that are bent toward the side of the circuit substrate 1 are produced,as shown in FIG. 3. Paths of the magnetic fluxes bent toward the side ofthe circuit substrate 1 is along an original path of the magnetic fluxesand the magnetic fluxes can pass through the magnetic core 2 moreeasily, which is more preferable. Although the curved portions 20 and 21are preferably provided at both ends of the magnetic core 2 of theantenna device 100, the curved portions are not necessarily disposed atboth ends. In addition, one end of the magnetic core 2 may be benttoward the side of the circuit substrate 1, while the other end may bebent away from the side of the circuit substrate 1. However, providingcurved portions that curve toward the side of the circuit substrate 1 atboth sides is more effective, and thus, more preferable.

Since winding directions of the coil portion A and the coil portion Bare opposite to one another, a direction of the current inducted by themagnetic flux 300 at the coil portion A and flowing around the coil axisis substantially the same as a direction of the current induced by themagnetic flux 301 at the coil portion B and flowing around the coilaxis. Since the coil portion A and the coil portion B are connected bythe connecting conductor 6 so that the right end of the coil portion Aand the left end of the coil portion B is connected as shown in FIG. 2,the current induced in the coil portion A and the current induced in thecoil portion B are not cancelled out. This enables a high-level signalto be extracted from the terminal 7 and the terminal 8.

Although a ground electrode is preferably provided on a surface facing asurface of the circuit substrate 1 on which the magnetic core 2 ismounted in this preferred embodiment, for example, a configuration inwhich a ground electrode is provided on a middle layer of a multilayercircuit substrate provides advantages that are similar to those of theabove-described preferred embodiments. In addition, the coil conductor 4defining the coil portion A, the coil conductor 5 defining the coilportion B, and the connecting conductor 6 may be defined by differentcopper wires, and may be electrically connected to each other bysoldering, for example. Furthermore, although the coil portion A and thecoil portion B are serially connected in this preferred embodiment, thecoil portion A and the coil portion B may be connected in parallel.

A third preferred embodiment will be described next using FIG. 4. FIG. 4is a perspective view of an antenna device 101 that is a third preferredembodiment of the present invention. The same numerals are applied tothe same portions as those of FIG. 2, and the description thereof isomitted.

A coil portion A and a coil portion B are connected by a conductorpattern 30 provided on a circuit substrate 1. The conductor pattern 30can preferably be formed on the circuit substrate 1 by pattern printing,for example. An end of the coil portion A and an end of the conductorpattern 30, and an end of the coil portion B and the other end of theconductor pattern 30 are preferably soldered, for example. Here, anexample in which a winding direction of the coil portion A around thecoil axis and a winding direction of the coil portion B around the coilaxis are the same direction is shown. The left end of the coil portion Aand the left end of the coil potion B is connected by the conductorpattern 30 as shown in FIG. 4 so that the current induced in the coilportion A and the current induced in the coil portion B by magneticfluxes as shown in FIG. 3 are not cancelled. In the third preferredembodiment, as in the second preferred embodiment, the coil portion Aand the coil portion B may be connected using a connecting conductorprovided on a magnetic core 2. However, when such a configuration isused, since the current may flow into locations other than the ends ofthe coil portions A and B due to crossing of the connecting conductorprovided on the magnetic core 2 and the coil portions A and/or B,insulating layers must be provided at the crossing portions.

The magnetic core 2 includes curved portions 22 and 23 whose shapes aredifferent from those of the antenna device 100. The curved portions 22and 23 are provided along lateral surfaces of a circuit substrate 1.When the configuration of the antenna device 101 is used, a CC-crosssection and a DD-cross section corresponding to FIG. 3 are furtherenlarged, which further reduces the magnetic reluctance at the ends ofthe magnetic core 2, enabling magnetic fluxes to pass through moreeasily and increasing the sensitivity of the antenna. In addition, aneffect of bending magnetic fluxes toward the side of the circuitsubstrate is also increased, which is preferable.

A fourth preferred embodiment will be described next using FIG. 5. FIG.5 is a perspective view of an antenna device 102 that is a fourthpreferred embodiment of the present invention. The same numerals areapplied to the same portions as those of FIG. 2, and the descriptionthereof is omitted.

The right end of a coil portion A and the left end of a coil portion Bare connected by a conductor pattern 31 provided on a circuit substrate1. Here, as in the second preferred embodiment, a winding direction ofthe coil portion A around the coil axis and a winding direction of thecoil portion B around the coil axis are opposite to one another. Theantenna device 102 of the fourth preferred embodiment is different fromthe second preferred embodiment in that the coil portion A and the coilpotion B are connected using a conductor pattern 31 provided on thecircuit substrate 1 but not using a conductor provided on a magneticcore 2 and in that the magnetic core 2 preferably includes two-stepcurved portions 24 and 25 at both ends thereof. The curved portion mayhave three or more steps, for example. This can prevent a crack that mayoccur during forming and burning of the magnetic core. Advantagesregarding electric characteristics are substantially the same as thoseof the second preferred embodiment.

A fifth preferred embodiment will be described next using FIG. 6. FIG. 6is a perspective view of an antenna device 103 that is a fifth preferredembodiment of the present invention. The same numerals are applied tothe same portions as those of FIG. 2, and the description thereof isomitted.

A configuration of a coil portion A, a coil portion B, and a connectingconductor 6 are substantially the same as that of the second preferredembodiment. Both ends of a magnetic core 2 curve without a sharp cornerto define curved portions 26 and 27. The magnetic core having such ashape can be produced by first pressing or molding a magnetic core intoa plate shape in the course of forming of the magnetic core 2, andburning the magnetic core after performing the bending in an unsinteredstate. Since a die cost is cheaper than pressing complex shapes, such asthose in the third preferred embodiment and the fourth preferredembodiment, the magnetic core can be inexpensively produced. Advantagesregarding electric characteristics are substantially the same as thoseof the second preferred embodiment.

A sixth preferred embodiment will be described next using FIG. 7. FIG. 7is a perspective view of an antenna device 104 that is a sixth preferredembodiment of the present invention. The same numerals are applied tothe same portions as those of FIG. 6, and the description thereof isomitted.

The antenna device 104 includes two divided magnetic cores 40 and 41. Acoil portion A is provided on the magnetic core 40 using a coilconductor 4, and a coil portion B is provided on the magnetic core 41using a coil conductor 5. The coil potions define a pair of coils. Themagnetic cores 40 and 41 are mounted on a circuit substrate so as to bespaced apart from each other by a predetermined interval e so that coilaxes of the coil portion A and the coil portion B are substantiallycoincident with one another. The right end of the coil portion A and theleft end of the coil portion B are connected by a conductor pattern 32provided on the circuit substrate. The configuration other than thedivision of the magnetic cores and the connection of the coil portion Aand the coil portion B by the conductor pattern 32 disposed on thecircuit substrate is substantially the same as that of the fifthpreferred embodiment. Such a configuration enables the magnetic core 40having the coil portion A provided thereon and the magnetic core 41having the coil portion B provided thereon to include substantially thesame components. Since the configuration of each coil is simple, thisconfiguration has an advantage in mass production and the antenna devicecan be inexpensively produced.

Since magnetic fluxes extending to a circuit substrate 1 perpendicularlyor substantially perpendicularly from above the circuit substrate 1cannot penetrate a ground electrode disposed on the circuit substrate 1,the magnetic fluxes are bent in a direction along a surface of thecircuit substrate 1 at a non-coil portion 50. The bent magnetic fluxespass into the magnetic cores from ends 51 and 52 of the magnetic coreson the circuit substrate 1, and induce the current in the coil portion Aand the coil portion B. A conceptual diagram of magnetic fluxes passingthrough the antenna device 104 is substantially the same as that shownin FIG. 3.

A seventh preferred embodiment will be described next using FIG. 8. FIG.8 is a perspective view of an antenna device 108 that is a seventhpreferred embodiment of the present invention. The same numerals areapplied to the same portions as those of FIG. 7, and the descriptionthereof is omitted.

A method for forming magnetic cores 40 and 41 and coil portions A and Bis substantially the same as that of the sixth preferred embodiment. Apoint different from the sixth preferred embodiment is that coil axes ofthe coil portion A and the coil portions B differ, i.e. are notsubstantially coincident with one another. The magnetic core 40 and themagnetic core 41 are arranged on a circuit substrate 1 so that a coilcross section of the coil A and a coil cross section of the coil Bprojected onto a given plane perpendicular or substantiallyperpendicular to the coil axes include an overlapping portion and anon-overlapping portion. By shifting the locations of the magnetic core40 and the magnetic core 41, the coil axes of the coil portion A and thecoil portion B are also shifted. Such an arrangement method enables fineadjustment of the mounting locations of the separate magnetic cores 40and 41, thus increasing the design flexibility of circuit substrates.

In addition, the antenna device 108 according to this preferredembodiment does not have any significant deterioration of communicationdistance as compared to the antenna device according to the sixthpreferred embodiment. This is because the number magnetic fluxes, amongmagnetic fluxes passing between the magnetic core 40 and the magneticcore 41, that are not led into the coil portion A and the coil portion Bis extremely low since the magnetic cores are mounted on the circuitsubstrate 1 so that the coil cross section of the coil portion A and thecoil cross section of the coil portion B projected onto the given planeperpendicular or substantially perpendicular to the coil axes have anoverlapping portion and a non-overlapping portion when viewed from thecoil axis direction.

Although the arrangement locations of the magnetic cores 40 and 41 arepreferably shifted in a direction perpendicular or substantiallyperpendicular to the coil axis along the circuit substrate 1 in theabove-described preferred embodiment, the present invention is notlimited to this preferred embodiment. For example, the location of eachmagnetic core may be shifted in a direction perpendicular orsubstantially perpendicular to a principal surface of a circuitsubstrate so that distances between each magnetic core and the circuitsubstrate differ or the location of each magnetic core may be shifted indifferent direction so as to shift the coil axes.

An eighth preferred embodiment will be described with reference to FIG.9. FIG. 9 is a sectional view along a coil axis of an antenna device 107that is an eighth preferred embodiment of the present invention. Thispreferred embodiment shows a sectional view when a magnetic core 2 isnot adhered to a circuit substrate 1 in the antenna device 102 that isthe fourth preferred embodiment shown in FIG. 5. The same numerals areapplied to the same portions as those of FIG. 5, and the descriptionthereof is omitted. Although the coil portion A and the coil portion Bare connected with the conductor pattern 31 disposed on the circuitsubstrate 1 in the fourth preferred embodiment, a coil portion A and acoil portion B are preferably connected by a connecting conductordisposed on a lateral surface of a magnetic core 2 in this preferredembodiment as in the fifth preferred embodiment shown in FIG. 6.Additionally, the sections of coil conductors 4 and 5 are omitted fromFIG. 9.

In this preferred embodiment, a description is provided of a sectionaldiagram of a casing 70 of a mobile phone. The casing 70 is preferablymade of a resin or other suitable material that allows magnetic fluxesto pass. A magnetic core 2 is fixed to the casing 70 with fixing members75 and 76. An adhesive or a double-sided adhesive tape is preferable asthe fixing member, for example. In addition, the magnetic core may bemechanically fixed to a suitable holder disposed on the casing 70.Preferably, a member that does not directly transmit an impact imposedon the casing 70 to the magnetic core 2 and that has the elasticity forabsorbing the linear expansion of the casing 70 and the magnetic core 2is used as the fixing member. When the magnetic core 2 is fixed to thecasing 70 as described above, a gap 400 is provided between the circuitsubstrate 1 and the magnetic core 2. Although electronic components tobe mounted on the circuit substrate 1, such as, for example, an IC, acapacitor, an inductor, and a filter, for example, are provided in thegap 400, the illustration thereof is omitted.

It is assumed that a reader/writer is arranged at the upper side of thisdrawing. Magnetic fluxes 302 extending from the upper side of thedrawing penetrate the casing 70, and pass into the magnetic core 2 froma non-coil portion 3 of the magnetic core 2. As described in FIG. 3,when the magnetic core 2 is arranged close to the circuit substrate 1,magnetic fluxes are shielded by a ground surface disposed on the circuitsubstrate 1 and are guided to the magnetic core 2, whereby the currentis induced. When a gap 200 is provided, as in this preferred embodiment,and the magnetic core 2 does not have an electrode for shieldingmagnetic fluxes, a portion of the magnetic fluxes 302 passing into themagnetic core 2 passes through the magnetic core 2, reaches the groundsurface of the circuit substrate 1, is shielded by the ground surface,and is guided to the gap 400. In this preferred embodiment, a shieldingelectrode 68 is preferably disposed on substantially an entire surfaceof the magnetic core 2 facing the circuit substrate 1. The shieldingelectrode 68 may preferably be formed according to a method for affixinga plate of a conductive member to the magnetic core 2 or a method forcoating a conductive paste onto the magnetic core 2, for example. Themagnetic fluxes 302 cannot penetrate the magnetic core 2 due to theshielding electrode 68, and are divided into a magnetic flux 303 passingto the left side of the magnetic core 2 and a magnetic flux 304 passingto the right side of the magnetic core 2. As described in FIG. 3, themagnetic flux 303 and the magnetic flux 304 induce the currents in thecoil portion A and the coil portion B. Since the shielding electrode 68must be electrically insulated from the coil conductors 4 and 5, theshielding electrode 68 is preferably disposed on the magnetic core 2through an insulating layer defined by an insulating adhesive, forexample. It is preferable that the shielding electrode 68 is disposed onthe magnetic core 2 through an insulating layer of low magneticpermeability even at the non-coil portion 3 not including the coilconductor 4 or 5 so as not to reduce the Q value of the coil portions Aand B functioning as an antenna. The shielding electrode 68 does notneed to cover substantially the entire surface of the magnetic core 2that faces the circuit substrate 1. In addition, the shielding electrode68 may preferably be extended to a lateral surface of the magnetic core2 if required.

Although an example that end surfaces 9 and 10 not defining the curve ofthe magnetic core 2 are arranged to be outside of a mounting surface ofthe circuit substrate 1 is shown in this preferred embodiment, the endsurfaces 9 and 10 may be arranged over the mounting surface of thecircuit substrate 1. However, when the end surfaces 9 and 10 are notarranged over the mounting surface of the circuit substrate 1 and arelocated outside of the circuit substrate 1 in plan view, the magneticfluxes 303 and 304 having induced the current in the coil portion A andthe coil portion B are radiated to the outside from the surface of thecurved portions 24 and 25 including the end surfaces 9 and 10.Accordingly, since an area from which the magnetic fluxes are radiatedis increased and the radiation efficiency of the magnetic fluxes isimproved, it is more preferable to arrange the end surfaces 9 and 10outside of the mounting surface.

A ninth preferred embodiment will be described with reference to FIGS.10 and 11. FIG. 10 is a perspective view of an antenna device 109 thatis a ninth preferred embodiment of the present invention. FIG. 11 is aplan view of a flexible substrate defining the antenna device 109 thatis the ninth preferred embodiment of the present invention. In thispreferred embodiment, a coil conductor is provided on an insulatingflexible substrate 80 preferably made of polyimide or other suitablematerial, and the flexible substrate is wound around a magnetic core 2,whereby a coil is formed. A configuration excluding the coil formingmethod is substantially the same as that of the second preferredembodiment.

The flexible substrate 80 is wound around a portion of the magnetic core2 excluding curved portions 20 and 21 disposed at the ends thereof. Asshown in FIG. 11, the flexible substrate 80 has a substantiallyrectangular principal surface. Conductor patterns 84 defining a coilportion A and conductor patterns 85 defining a coil portion B areprovided at both sides of the principal surface excluding the centralportion so as to connect an upper end and a lower end of the flexiblesubstrate 80. Each of the conductor patterns 84 and 85 includes a bentportion 82 near the approximate center thereof. In addition, twoconductor patterns located at innermost locations on the principalsurface of the flexible substrate 80 among the conductor patterns 84 and85 provided on both sides excluding the central portion are connected bya conductor pattern 86 defining a connecting conductor. The conductorpatterns 84, 85, and 96 can preferably be formed by screen printing oretching, for example. The flexible substrate 80 is wound around themagnetic core 2 with the surface having the conductor patterns 84 and 85being inside such that the upper ends and the lower ends of theconductor patterns 84 and 85 defining the coil portion A and the coilportion B sequentially overlap. The overlapping portions areelectrically connected, for example, by soldering. In this manner, theconductor patterns 84 and 85 define a series of coils as shown in FIG.10. Although the conductor patterns 84, 85, 86 are shown as a singleline in FIG. 10, the conductor patterns have a predetermined width asshown in FIG. 11. The flexible substrate 80 can preferably be fixedaround the magnetic core 2 by soldering or other suitable method. Byadhering the flexible substrate 80 on the magnetic core 2 with anadhesive, stable production is possible. The flexible substrate 80 maybe wound around the magnetic core 2 so that the surface having theconductor patterns 84 and 85 is located outside. However, when thesurface having the conductor patterns 84 and 85 is located inside, theconductor patterns are much less likely to peel off, which is thus morepreferable.

Since formation of a coil according to such a method eliminates the needto print conductors on a magnetic core, the coil conductors can beinexpensively formed. In addition, when an electrode is formed directlyon a magnetic core, there is a problem in that the Q value of the coilsfunctioning as an antenna decreases. When an insulating flexiblesubstrate having low magnetic permeability is used, the Q value isimproved, which is thus more preferable.

In addition, shapes of the conductor patterns 84, 85, and 86 provided onthe flexible substrate 80 are not limited to the one described above.

A tenth preferred embodiment will be described with reference to FIG. 12and FIG. 13. FIG. 12 is a perspective view of an antenna device 110 thatis a tenth preferred embodiment of the present invention. FIG. 13 is aplan view of a flexible substrate defining the antenna device 110 thatis the tenth preferred embodiment of the present invention. As in theninth preferred embodiment, a flexible substrate having coil conductorsprovided thereon is wound around a magnetic core, whereby a coil isprovided in this preferred embodiment. The tenth preferred embodiment isdifferent from the ninth preferred embodiment in that the flexiblesubstrate is also wound around curved portions to form coils and in thatthe magnetic core is divided into two portions.

The antenna device 110 includes two divided magnetic cores 90 and 91.Curved portions 92 and 93 are provided at the left end of the magneticcore 90 and the right end of the magnetic core 91. One flexiblesubstrate 94 is wound around the magnetic cores 90 and 91. The flexiblesubstrate 94 also covers the curved portions 92 and 93.

As shown in FIG. 13, the flexible substrate 94 includes three notches 97a, 97 b, and 97 c and one protrusion 98. Conductor patterns 95 defininga coil A and conductor patterns 96 defining a coil B are provided onboth sides of a principal surface of the flexible substrate 94 excludinga central portion so as to be connected to a lower end of the flexiblesubstrate 94 but not to be connected to an upper end thereof. Theconfiguration of each conductor pattern is substantially the same asthat of the ninth preferred embodiment. A conductor pattern 99 arrangedto be connected to a terminal (not shown) is disposed near the upper endof the flexible substrate 94, and extends to an end portion of theprotrusion 98 of the flexible substrate 94. A conductor pattern of theprotrusion 98 is connected to an external terminal (not shown).

The flexible substrate 94 is bent along the curved portions 92 and 93 ofthe magnetic cores 90 and 91. Thereafter, the flexible substrate 94 iswound around the magnetic cores 90 and 91 so that upper ends and lowerends of the conductor patterns 95 and 96 defining the coil A and thecoil B sequentially overlap. The overlapping portions are electricallyconnected by soldering, for example. In this manner, the conductorpatterns 95 and 96 define a series of coils.

Formation of a coil according to such a method enables coil conductorsto be easily formed at the curved portions 92 and 93 of the magneticcore 90 and 91. When the coil conductors are formed at the curvedportions 92 and 93, advantages similar to those obtained when the lengthof the coil is increased can be obtained, and the sensitivity of theantenna can be improved.

Although three notches 97 a, 97 b, and 97 c are preferably provided onthe flexible substrate 94 in the antenna device 110, for example, thenotches are not necessarily provided. However, since the notch 97 blocated at the approximate center of the flexible substrate 94 generatesa space between the circuit substrate 1 and the flexible substrate 94and enables other circuit components to be mounted, it is preferable toprovide the notch. In addition, since the notches 97 a and 97 c providedbetween the conductor patterns 95 defining the coil A and between theconductor patterns 96 defining the coil B facilitate winding of theflexible substrate 94 around the magnetic cores 90 and 91, it ispreferable to provide the notches.

As a preferred embodiment of the present invention that is not describedin any of the above-described preferred embodiments, a coil portion Aand a coil portion B can be connected using a substrate that isdifferent from a circuit substrate 1 in the fifth preferred embodimentshown in FIG. 6. In this case, both of a coil conductor defining thecoil portion A and a coil conductor defining the coil portion B isprovided on a flexible substrate having the above-described coilconductors thereon. Furthermore, a connecting conductor arranged toconnect these coils may be provided on the flexible substrate.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. An antenna device comprising: an antenna coil including a magneticcore having a first principal surface, a second principal surface facingthe first principal surface, and a curved portion at at least one end ofthe magnetic core, and a coil provided on the first principal surface ofthe magnetic core, a coil axis of the coil being substantiallyperpendicular to the first principal surface, and an opening beingdisposed at the approximate center of the coil; and a planar electrode;wherein the antenna coil is arranged to radiate magnetic flux; thecurved portion is curved in a direction such that the magnetic flux isbent towards a side of the planar electrode and a path of the magneticflux extends to the side of the planar electrode; and the antenna coilis arranged such that the second principal surface of the magnetic corefaces a surface of the planar electrode.
 2. The antenna device accordingto claim 1, wherein the curved portion is arranged to extend in adirection along a lateral surface of the planar electrode.
 3. Theantenna device according to claim 2, wherein at least a portion of anend surface of the magnetic core is located outside the planar electrodein a plan view.
 4. The antenna device according to claim 1, wherein theantenna coil is arranged on the planar electrode with a spacetherebetween.
 5. The antenna device according to claim 1, wherein aflexible substrate having an electrode pattern provided thereon is woundaround the magnetic core to define the coil.
 6. The antenna deviceaccording to claim 1, wherein the antenna coil is arranged directly onthe planar electrode.
 7. The antenna device according to claim 1,wherein the curved portion is provided at one end of the magnetic core.8. The antenna device according to claim 1, wherein a plurality of thecurved portions is provided at two opposite ends of the magnetic core.